Magnetic storage element

ABSTRACT

A magnetic storage element includes a first magnetic layer having a magnetization easy axis in a direction perpendicular to a surface of the first magnetic layer. A first non-magnetic layer is on the first magnetic layer. A second magnetic layer is on the first non-magnetic layer and has a fixed magnetization direction. A second non-magnetic layer is on the second magnetic layer. A third magnetic layer is on the second non-magnetic layer and has a fixed magnetization direction perpendicular to a surface of the third magnetic layer. A third non-magnetic layer is on the third magnetic layer. A storage layer on the third non-magnetic layer and having a variable magnetization direction with a magnetization easy axis in a direction perpendicular to a surface of the storage layer. Change in a magnetization direction of the first magnetic layer is easier than in the storage layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application under 35 U.S.C. 371 andclaims the benefit of PCT Application No. PCT/JP2015/009571 having aninternational filing data of 9 Mar. 2017, which designated the UnitedStates, which PCT application claimed the benefit of Japanese PriorityPatent Application JP 2016-084336 filed Apr. 20, 2016, the entirecontents of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a magnetic storage element.

BACKGROUND ART

As performances of various types of information devices are improved inrecent years, performances of storage devices and computation processingdevices provided in these various types of information devices are alsobeing improved.

For example, in non-volatile semiconductor storage elements used in thestorage devices or the like, improvements such as high integration, highspeed, and low electric power consumption are in progress. Also, for thepurpose of further performance improvement, development of various typeof semiconductor storage elements, such as ferroelectric random accessmemory (FeRAM), phase-change random access memory (PCRAM), and magneticrandom access memory (MRAM), in addition to flash memory is in progress.

The MRAM that stores information by magnetization directions of amagnetic body is capable of high speed operation, and has a high storagereliability, and thus is attracting attention as a storage elementsuperior to the flash memory. In particular, of the MRAMs, a magneticstorage element which is referred to as a spin transfer torque-magneticrandom access memory (STT-MRAM) that reverses magnetization directionsof a magnetic layer by injecting a spin-polarized electron in themagnetic layer is attracting attention.

Here, in the STT-MRAM, in order to decrease write errors to improve thereliability as the storage element, an applied voltage at the time ofwrite (i.e., electric current at the time of write) is increased, andthe probability of reversing the magnetization direction of the magneticlayer is increased.

Note that, in the STT-MRAM, when the applied voltage at the time ofwrite is a certain value or more, a phenomenon which is referred to aslow probability bifurcated switching (LPBS) in which a write error rateis difficult to decrease occurs due to magnetic inhomogeneity of themagnetic body. When the LPBS occurs, a higher voltage is to be appliedat the time of write in order to satisfy the write error rate necessaryas the storage element, and thus electric power consumption increases atthe time of write.

For example, the below Patent Literature 1 discloses signal processingof the voltage at the time of write in order to decrease the write errorrate of the STT-MRAM.

CITATION LIST Patent Literature

PTL 1: US Patent Application Publication No. 2014/0347918

SUMMARY Technical Problem

However, in order to employ the technology disclosed in PatentLiterature 1, it is necessary to separately add a circuit for performingsignal processing of the voltage at the time of write into the magneticstorage element that configures the STT-MRAM. Hence, in the magneticstorage element that employs the technology disclosed in PatentLiterature 1, the circuit size increases, and the integration degreedecreases.

Thus, the present disclosure proposes a new and improved magneticstorage element that can be driven with lower electric powerconsumption, by reducing the LPBS, without decreasing the integrationdegree.

Solution to Problem

According to an embodiment of the present disclosure, there is provideda magnetic storage element including: a storage layer that has amagnetization easy axis in a perpendicular direction to a film surface,a magnetization direction of the storage layer being variable; areference layer provided at least one surface side of the storage layerwith a non-magnetic layer in between, and having magnetization whosedirection is fixed in one direction perpendicular to a film surface; amagnetization fixation layer provided at a surface side opposite to asurface of the reference layer at which the storage layer is provided,with a non-magnetic layer in between, and having magnetization whosedirection is fixed in an antiparallel direction to a magnetizationdirection of the reference layer; and a magnetization assist layerprovided at a surface side opposite to a surface of the magnetizationfixation layer at which the reference layer is provided, with anon-magnetic layer in between, and having a magnetization easy axis in aperpendicular direction to a film surface, in which change in amagnetization direction is easier than in the storage layer.

According to an embodiment of the present disclosure, there is provideda magnetic storage element including: a storage layer that storesinformation by a magnetization direction; a reference layer whosemagnetization direction is fixed, the reference layer serving as areference for the magnetization direction of the storage layer; amagnetization fixation layer that magnetically couples with thereference layer; and a magnetization assist layer in which change in amagnetization direction is easier than in the storage layer. Wheninformation is written into the storage layer by a spin torque generatedby an electric current that flows through the storage layer, thereference layer, the magnetization fixation layer, and the magnetizationassist layer, the magnetization assist layer reverses magnetization in aparallel direction to the magnetization direction written into thestorage layer, and applies an external magnetic field to the storagelayer.

According to an embodiment of the present disclosure, when informationis written, an external magnetic field parallel to the magnetizationreversal direction of the storage layer is applied to the storage layerby the magnetization assist layer, thereby reducing occurrence of theLPBS that makes it difficult to decrease the write error rate.

Advantageous Effects of Invention

As described above, according to the present disclosure, the LPBS isreduced (or alternatively, prevented) without decreasing the integrationdegree of magnetic storage elements, enabling driving with lowerelectric power consumption.

Note that the effects described above are not necessarily limitative.With or in the place of the above effects, there may be achieved any oneof the effects described in this specification or other effects that maybe grasped from this specification.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory diagram that schematically illustrates astacking structure of a magnetic storage element according to anembodiment of the present disclosure.

FIG. 2A is an explanatory diagram illustrating behavior at the time of Lwrite of a magnetic storage element according to the embodiment.

FIG. 2B is an explanatory diagram illustrating behavior at the time of Hwrite of a magnetic storage element according to the embodiment.

FIG. 3 is an explanatory diagram that schematically illustrates astacking structure of a magnetic storage element according to a firstexemplary variant.

FIG. 4 is an explanatory diagram that schematically illustrates astacking structure of a magnetic storage element according to a secondexemplary variant.

FIG. 5 is an explanatory diagram that schematically illustrates astacking structure of a magnetic storage element according to a thirdexemplary variant.

FIG. 6 is an explanatory diagram illustrating a layer structure of amagnetic storage element according to working example 1.

FIG. 7 is an explanatory diagram illustrating a layer structure of amagnetic storage element according to a comparative example.

FIG. 8 is a graph diagram that illustrates a relationship between awrite error rate of a magnetic storage element according to workingexample 1 and an applied voltage.

FIG. 9 is a graph diagram that illustrates a relationship between awrite error rate of a magnetic storage element according to acomparative example and an applied voltage.

FIG. 10 is an explanatory diagram illustrating a layer structure of amagnetic storage element according to working example 2.

FIG. 11 is an explanatory diagram illustrating a layer structure of amagnetic storage element according to working example 3.

FIG. 12 is an explanatory diagram illustrating a layer structure of amagnetic storage element according to working example 4.

FIG. 13 is an explanatory diagram illustrating a layer structure of amagnetic storage element according to working example 5.

FIG. 14 is an explanatory diagram illustrating a layer structure of amagnetic storage element according to working example 6.

FIG. 15 is an explanatory diagram illustrating a layer structure of amagnetic storage element according to working example 7.

FIG. 16 is an explanatory diagram illustrating a layer structure of amagnetic storage element according to working example 8.

FIG. 17 is an explanatory diagram that schematically illustrates astacking structure of a magnetic storage element of an STT-MRAM.

FIG. 18 is a graph diagram illustrating a relationship between a writeerror rate of a magnetic storage element and an applied voltage when anLPBS occurs.

FIG. 19A is a graph diagram that illustrates a relationship between awrite error rate when an external magnetic field is not applied and anapplied voltage.

FIG. 19B is a graph diagram that illustrates a relationship between awrite error rate when an external magnetic field is applied and anapplied voltage.

FIG. 19C is a graph diagram that illustrates a relationship between awrite error rate when an external magnetic field is applied and anapplied voltage.

DESCRIPTION OF EMBODIMENTS

Hereinafter, (a) preferred embodiment(s) of the present disclosure willbe described in detail with reference to the appended drawings. In thisspecification and the appended drawings, structural elements that havesubstantially the same function and structure are denoted with the samereference numerals, and repeated explanation of these structuralelements is omitted.

Note that description will be made in the following order.

1. Background of Present Disclosure

1.1. Technical Background of Present Disclosure

1.2. Configuration of Magnetic Storage Element of STT-MRAM

1.3. Study of Error Rate Characteristics at Time of Write

2. Embodiment of Present Disclosure

2.1. Configuration of Magnetic Storage Element

2.2. Exemplary Variant

3. Working Example of Present Disclosure

4. Conclusion

1. BACKGROUND OF PRESENT DISCLOSURE

(1.1. Technical Background of Present Disclosure)

First, the technical background of the present disclosure will bedescribed. The technology according to the present disclosure relates toa non-volatile semiconductor storage element that stores various typesof information.

The non-volatile semiconductor storage element is making marked advanceas represented by a flash memory, and its development is in progresswith such a momentum as to expel storage devices other than thesemiconductor storage element, such as a hard disk drive (HDD) device.Also, there is a study to develop a storage device composed ofnon-volatile semiconductor storage elements into a code storage thatstores programs, calculation parameters and the like, and a workingmemory that temporarily stores parameters that change as appropriateduring execution of a program and the like, in addition to a datastorage.

Although a NOR or NAND flash memory represents this non-volatilesemiconductor storage element as described above, a FeRAM that storesinformation by remnant polarization of ferroelectric, a PCRAM thatstores information by phase states of a phase-change film, and an MRAMthat stores information by magnetization directions of a magnetic body,and the like are developed as well.

In particular, the MRAM stores information by magnetization directionsof a magnetic body, and thus can perform rewrite of the information at ahigh speed and almost without limitation. Hence, the MRAM is underintensive development, and is partially put into practical use in fieldssuch as an industrial automation device and a plane.

Note that, of MRAMs, an MRAM that reverses magnetization of the magneticbody by an electric current magnetic field generated from a line hasdifficulty in reducing electric power consumption and making thecapacity larger, due to the above method of reversing magnetization.This is because, in order to generate the electric current magneticfield of the intensity that can reverse the magnetization of themagnetic body, an electric current of approximately several mA isnecessary, and the electric power consumption at the time of writeincreases. Also, it is necessary to prepare a line that generates anelectric current magnetic field for each magnetic storage element, andthere is a limitation to size reduction of the magnetic storage element.

Thus, there is a study of an MRAM that can reverse the magnetization ofthe magnetic body by a method other than using the electric currentmagnetic field from the line. Specifically, there is a study of an MRAMthat reverses the magnetization of the magnetic body by using spintorque magnetization reversal.

The spin torque magnetization reversal is a magnetization reversalmethod that, when a spin-polarized electron that has passed through amagnetic body having a magnetic moment fixed to a predetermineddirection enters another magnetic body, imparts a torque to the magneticmoment of the entered magnetic body. Thereby, the magnetic moment of themagnetic body, in which the electric current (i.e., the spin-polarizedelectron) equal to or larger than a threshold value flows and to whichthe torque equal to or larger than a threshold value is imparted,reverses in the direction parallel to the imparted torque. Note that thereversal direction of the magnetic moment is controllable by changingthe polarity of the electric current that flows in the magnetic body.

Here, the absolute value of the electric current necessary to generatethe spin torque magnetization reversal is approximately 100 μA or lessfor the magnetic storage element of the size of approximately 50 nm, anddecreases as the volume of the magnetic storage element becomes smaller.On the other hand, when the magnetization of the magnetic body isreversed by using the electric current magnetic field generated from theline, the electric current necessary for the magnetization reversal isapproximately several mA. Thus, the MRAM that uses the spin torquemagnetization reversal (also referred to as STT-MRAM) can make theelectric current at the time of the write extremely smaller than theMRAM that uses the magnetization reversal by the electric currentmagnetic field from the line, and thereby is capable of operating withlow electric power consumption.

Also, the line, such as a word line, that generates the electric currentmagnetic field is necessary in the MRAM that uses the magnetizationreversal by the electric current magnetic field from the line, but thisline becomes unnecessary in the STT-MRAM. Hence, the STT-MRAM can reducethe size of each magnetic storage element as compared to the MRAM thatuses the magnetization reversal by the electric current magnetic fieldfrom the line, and thereby can make the capacity larger.

Thus, the STT-MRAM can make the electric power consumption lower and thecapacity larger, while maintaining the characteristics of the MRAM thatcan rewrite information at a high speed and almost without a limitation,and thus is attracting considerable attention as a high-performancenon-volatile semiconductor storage element.

(1.2. Configuration of Magnetic Storage Element of STT-MRAM)

Next, with reference to FIG. 17, a structure of each magnetic storageelement of the STT-MRAM that uses the spin torque magnetization reversaldescribed above will be described. FIG. 17 is an explanatory diagramthat schematically illustrates a stacking structure of a magneticstorage element of the STT-MRAM.

As illustrated in FIG. 17, a magnetic storage element 10 of the STT-MRAMincludes a first electrode layer 11, a magnetization fixation layer 14,a magnetization coupling layer 15, a reference layer 16, a spininjection layer 17, a storage layer 18, and a second electrode layer 19.

The magnetic storage element 10 is one storage element that stores onepiece of information (0 or 1). Address lines (i.e., a word line and abit line) orthogonal to each other are provided above and below themagnetic storage element 10, and the magnetic storage element 10 isconnected to the word line and the bit line near the intersection pointof the lines.

Specifically, in the magnetic storage element 10, the first electrodelayer 11 and the word line are connected, and the second electrode layer19 and the bit line are connected, via a selection transistor or thelike. Thereby, in the magnetic storage element 10 selected by theselection transistor, voltage is applied between the first electrodelayer 11 and the second electrode layer 19 via the word line and the bitline, to perform rewrite and readout of the information stored in thestorage layer 18. Note that, in FIG. 17, the word line, the bit line,and the selection transistor are not depicted.

Note that FIG. 17 has illustrated a structure in which the spininjection layer 17, the reference layer 16, the magnetization couplinglayer 15, and the magnetization fixation layer 14 are stacked in thedownward direction with respect to the storage layer 18, as the stackingstructure of the magnetic storage element 10, but the magnetic storageelement 10 is not limited to this structure. The magnetic storageelement 10 may have a structure in which the spin injection layer 17,the reference layer 16, the magnetization coupling layer 15, and themagnetization fixation layer 14 are stacked in the upward direction withrespect to the storage layer 18.

The storage layer 18 is formed of a magnetic body includingferromagnetic material, and stores information by magnetizationdirections of the magnetic body. Also, the magnetization easy axis ofthe storage layer 18 is in the perpendicular direction to the filmsurface, and the storage layer 18 is provided such that themagnetization direction is variable. The storage layer 18 may be asingle layer, and may be stacked layers of non-magnetic layers andmagnetic layers, and may be stacked layers of oxide layers and magneticlayers.

The reference layer 16 is formed of a magnetic body includingferromagnetic material, and is provided at one surface side of thestorage layer 18 with the spin injection layer 17 in between. Themagnetization direction of the reference layer 16 is fixed in onedirection (in FIG. 17, the direction from the first electrode layer 11toward the second electrode layer 19), and functions as a reference forthe magnetization direction retained in the storage layer 18.

The spin injection layer 17 is formed of non-magnetic material, and isprovided and sandwiched between the storage layer 18 and the referencelayer 16. The spin injection layer 17 exchanges a spin-polarizedelectron with the storage layer 18 and the reference layer 16 at thetime of write of information into the storage layer 18, and therebyimparts a spin torque to the storage layer 18 and reverses themagnetization direction of the storage layer 18.

Also, the spin injection layer 17 changes the electrical resistance onthe basis of the magnetization direction of each of the storage layer 18and the reference layer 16 by magnetoresistance effect, at the time ofreadout of information from the storage layer 18. Thus, the magneticstorage element 10 can read out the information stored in the storagelayer 18, by measuring the electrical resistance between the firstelectrode layer 11 and the second electrode layer 19.

The magnetization fixation layer 14 is formed of a magnetic bodyincluding ferromagnetic material, and is provided at the surface sideopposite to the surface of the reference layer 16 on which the spininjection layer 17 is provided, with the magnetization coupling layer 15in between. The magnetization fixation layer 14 has magnetization fixedin the direction (in FIG. 17, the direction from the second electrodelayer 19 toward the first electrode layer 11) antiparallel to themagnetization of the reference layer 16, and cancels a leak magneticfield from the reference layer 16 by magnetically coupling with thereference layer 16. Thereby, the magnetization fixation layer 14 canreduce the magnetic influence from the reference layer 16 to the storagelayer 18.

The magnetization coupling layer 15 is formed of non-magnetic material,and is provided and sandwiched between the reference layer 16 and themagnetization fixation layer 14. The magnetization coupling layer 15 canstabilize the magnetization direction of the reference layer 16 bymagnetically coupling the reference layer 16 and the magnetizationfixation layer 14, and improve retention characteristics of themagnetization direction of the reference layer 16.

Note that the ferromagnetic material included in the storage layer 18,the reference layer 16, and the magnetization fixation layer 14 is, forexample, amorphous perpendicular magnetization material such as TbFeCoand GdFeCo, magnetic material having crystal magnetic anisotropy such asCoPt and FePt, or alloy magnetic material of at least one or moreselected from among Fe, Co, and Ni and at least one or more selectedfrom among B and C.

The first electrode layer 11 and the second electrode layer 19 areprovided to sandwich the magnetization fixation layer 14, themagnetization coupling layer 15, the reference layer 16, the spininjection layer 17, and the storage layer 18.

The first electrode layer 11 functions as a lower electrode of themagnetic storage element 10, and is formed of various types of metalmaterials or alloy materials. Also, the first electrode layer 11 maycontrol the crystal orientation of the magnetization fixation layer 14that is stacked on the first electrode layer 11. For example, the firstelectrode layer 11 may be formed of metal material whose crystalorientation and magnetic anisotropy are substantially identical with themagnetization fixation layer 14. Also, the second electrode layer 19functions as an upper electrode of the magnetic storage element 10, andis formed of various types of metals or alloys. Also, the secondelectrode layer 19 may function as a protection layer of the magneticstorage element 10.

Next, a scheme of write and readout of information in the magneticstorage element 10 will be described.

First, the scheme of readout of information in the magnetic storageelement 10 will be described. In the magnetic storage element 10,readout of information from the storage layer 18 is performed by usingthe magnetoresistance effect.

Specifically, when the electric current is flowed between the firstelectrode layer 11 and the second electrode layer 19, the electricalresistance of the spin injection layer 17 changes on the basis ofwhether the magnetization directions of the storage layer 18 and thereference layer 16 are in a parallel state or in an antiparallel state.Thereby, the information stored in the storage layer 18 can be read outby detecting the value of the electrical resistance indicated by themagnetic storage element 10.

Next, the scheme of write of information in the magnetic storage element10 will be described. In the magnetic storage element 10, write ofinformation into the storage layer 18 is performed by using spin torquemagnetization reversal. In the following, the spin torque magnetizationreversal will be described with a focus on the storage layer 18, thereference layer 16, and the spin injection layer 17.

First, the electron can take two different spin angular momenta, whichare provisionally defined as an upward direction and a downwarddirection respectively. Thus, the electrons in the upward direction andthe electrons in the downward direction are of the same number in anon-magnetic body, and a difference is generated between the number ofelectrons in the upward direction and the number of electrons in thedownward direction in a ferromagnetic body.

Here, a case is considered in which an electron is moved from thereference layer 16 to the storage layer 18, in the storage layer 18 andthe reference layer 16 whose magnetization directions are antiparallelto each other. In the reference layer 16, the magnetic moment is fixedby the magnetic coupling with the magnetization fixation layer 14, andthus the electrons that have passed through the reference layer 16generate a difference between the number of electrons in the upwarddirection and the number of electrons in the downward direction (alsoreferred to as spin polarization) in the same polarization direction asthe magnetic moment of the reference layer 16.

When the spin injection layer 17 is formed sufficiently thin, theelectrons that have passed through the reference layer 16 enter thestorage layer 18, before the spin polarization is relaxed and theelectrons in the upward direction and the electrons in the downwarddirection become the same number (also referred to unpolarized state).

The storage layer 18 has an inversed spin polarization direction to theentered electrons. Thus, the energy of the entire system is reduced, andthus a part of the entering electrons reverses the direction of the spinangular momentum. Note that the spin angular momentum is conserved inthe entire system, and thus counteraction equivalent to total change ofthe spin angular momenta of the reversed electrons is added to themagnetic moment of the storage layer 18.

When the electric current that flows in the reference layer 16 and thestorage layer 18 is small, the number of electrons per unit time thatenters the storage layer 18 is also small, and thus the total spinangular momentum added to the magnetic moment of the storage layer 18 isalso small. However, as the electric current amount that flows in thereference layer 16 and the storage layer 18 increases, the total spinangular momentum per unit time added to the magnetic moment of thestorage layer 18 becomes larger. Then, when the torque, which is thetemporal change of the angular momentum, exceeds a threshold value, themagnetic moment of the storage layer 18 starts a precessional motion,and thereafter becomes stabilized in a state in which the magneticmoment is reversed by 180°. Note that the magnetic moment of the storagelayer 18 is stabilized in the state in which the magnetic moment isreversed by 180°, because the magnetic body that configures the storagelayer 18 has a magnetization easy axis, and has uniaxial anisotropy.

With the above scheme, the magnetization direction of the storage layer18 is reversed to a parallel state, from the antiparallel state to thereference layer 16. Thus, in the magnetic storage element 10, themagnetization direction of the storage layer 18 whose magnetizationdirection is antiparallel to the reference layer 16 can be reversed byflowing the electric current from the storage layer 18 to the referencelayer 16 and injecting the electrons into the storage layer 18 from thereference layer 16.

On the other hand, when the magnetization direction of the storage layer18 whose magnetization direction is parallel to the reference layer 16is reversed, the electrons are injected into the reference layer 16 fromthe storage layer 18, by flowing the electric current from the referencelayer 16 to the storage layer 18. In this case, the electrons that enterthe reference layer 16 are reflected at the reference layer 16, andthereby the electrons reverse the spin and enter into the storage layer18 again. Thereby, the magnetic moment of the storage layer 18 receivestorque from the electrons whose spins are reversed by the reflection atthe reference layer 16, and thus when the torque exceeds a thresholdvalue, the magnetic moment of the storage layer 18 reverses in anantiparallel direction to the reference layer 16.

Note that the electric current amount necessary to reverse themagnetization direction of the storage layer 18 that has themagnetization direction parallel to the reference layer 16 becomeslarger than when reversing the magnetization direction of the storagelayer 18 that has the antiparallel magnetization direction. In thefollowing, for convenience, the write that reverses the magnetization ofthe storage layer 18 parallel to the magnetization direction of thereference layer 16 is referred to as “H write” because the necessaryelectric current amount is large, and the write that reverses themagnetization of the storage layer 18 antiparallel to the magnetizationdirection of the reference layer 16 is referred to as “L write”.

As described above, in the magnetic storage element 10, the write of theinformation into the storage layer 18 is performed by flowing theelectric current equal to or larger than a threshold value correspondingto the polarity of the electric current, in the storage layer 18, thespin injection layer 17, and the reference layer 16.

In more detail, the threshold value Ic₀ of the electric current (alsoreferred to as reversal electric current) necessary to reverse themagnetization of the storage layer 18 by the spin torque magnetizationreversal is expressed by the following equation 1A and equation 1B, whenthe magnetization easy axis of the storage layer 18 is directed in theperpendicular direction to the film surface. Note that equation 1A isthe equation when the magnetization of the storage layer 18 is parallelto the magnetization direction of the reference layer 16, and equation1B is the equation when the magnetization of the storage layer 18 isantiparallel to the magnetization direction of the reference layer 16.[Math.1]Ic ₀=(A·α·Ms·V/g(0)/P)Hk  equation 1AIc ₀=−(A·α·Ms·V/g(π)/P)Hk  equation 1B

In the above equation 1A and equation 1B, A is a constant; α is adumping constant; Ms is saturation magnetization; V is the volume of thestorage layer 18; P is a spin polarizability; g(0) and g(π) arecoefficients for the efficiency of transferal of the spin torquetransferred to the storage layer 18 in the parallel or antiparallelcase; and Hk is an effective anisotropic magnetic field.

Also, the reversal electric current Ic₀ can be expressed by thefollowing equation 2 in the relationship with the index Δ of the thermalstability of the magnetic body.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 2} \right\rbrack & \; \\{{Ic}_{0} = {\left( \frac{4\;{ek}_{B}T}{h} \right)\;\left( \frac{\alpha\;\Delta}{\eta} \right)}} & {{equation}\mspace{14mu} 2}\end{matrix}$

In the above equation 2, e is an electric charge of electron; η is aspin injection efficiency; h is a reduced Planck constant; α is adumping constant; k_(B) is a Boltzmann constant; and T is a temperature.Also, the index Δ of the thermal stability of the magnetic body isexpressed by the following equation 3.[Math.3]Δ=KV/k _(B) T=Ms·V·H _(k)·(½·k _(B) T)  equation 3

In the above equation 3, Hk is an effective perpendicular magneticanisotropy; k_(B) is a Boltzmann constant; T is a temperature; Ms is asaturation magnetization; V is the volume of the storage layer 18; and Kis anisotropic energy. Note that the effective anisotropic magneticfield H_(k) includes influence of magnetic shape anisotropy, inducedmagnetic anisotropy, and crystal magnetic anisotropy, but theanisotropic magnetic field H_(k) is equivalent to coercivity, assumingthe magnetization reversal of the storage layer 18 as a coherentrotation model of single magnetic domain.

In the magnetic storage element that stores information by themagnetization directions of the magnetic body, it is important tosimultaneously achieve the index Δ of the thermal stability and thereversal electric current Ic₀ which is the threshold value of themagnetization reversal. That is, in the magnetic storage element, it isnecessary to make the threshold value of the magnetization reversallower, while making the thermal stability higher. According to the aboveequations, the magnetic storage element 10, which is the STT-MRAM, canset the reversal electric current to approximately several ten toseveral hundred μA, even when sufficient thermal stability is ensured inthe storage layer 18 having a flat circular shape of diameter 50 nm anda thickness of 2 nm.

Thus, the magnetic storage element 10 that uses the spin torquemagnetization reversal can make the electric current at the time ofwrite smaller than the magnetic storage element that uses themagnetization reversal by the electric current magnetic field, andthereby can operate with low electric power consumption. Also, themagnetic storage element 10 that uses the spin torque magnetizationreversal is needless to have the line for generating the electriccurrent magnetic field as compared to the magnetic storage element thatuses the magnetization reversal by the electric current magnetic field,and can make the size of the element smaller, and thus can make thecapacity larger.

(1.3. Study of Error Rate Characteristics at Time of Write)

Next, the error rate characteristics at the time of write in themagnetic storage element 10 which is the STT-MRAM will be described withreference to FIGS. 18 to 19C.

In the magnetic storage element 10 that uses the spin torquemagnetization reversal to write the information, the reversal of themagnetization of the storage layer 18 occurs with a probabilityaccording to the size of the voltage (i.e., the electric current) thatis applied to the magnetic storage element 10. Thus, in the magneticstorage element 10, the proportion (write error rate) of the writeerror, which is a write failure of the information into the storagelayer 18, is predicted to decrease with the increase of the appliedvoltage.

Here, the degree of decrease of the write error rate in relation to theapplied voltage becomes more gradual as the pulse width of the signalused in the write of the information becomes shorter. Thus, when theshort pulse signal is used in the storage of the information, it isnecessary to make the applied voltage higher to achieve sufficiently lowwrite error rate.

Also, when the signal used in the write of the information is a shortpulse, a phenomenon which is referred to as low probability bifurcatedswitching (LPBS) in which the write error rate irregularly decreases inrelation to the applied voltage occurs in some cases, due to themagnetic inhomogeneity of the magnetic storage element 10. When the LPBSoccurs, the write error rate decreases more gradually in relation to theapplied voltage, and thus it is necessary to make the applied voltagehigher to achieve a sufficiently low write error rate.

A representative relationship between the write error rate of themagnetic storage element 10 and the applied voltage when the LPBS occursis illustrated in FIG. 18. FIG. 18 is a graph diagram illustrating therelationship between the write error rate of the magnetic storageelement 10 and the applied voltage when the LPBS occurs. Note that FIG.18 is in the case of H write, and the pulse width of the write signal isapproximately 15 ns.

In the magnetic storage element 10, the write error rate decreases withthe increase of the applied voltage, as illustrated in FIG. 18. However,the decrease of the write error rate becomes gradual in relation to theincrease of the applied voltage, from a boundary at the applied voltagenear 0.3V.

This LPBS occurs due to the magnetic inhomogeneity of the magneticstorage element 10, and thus does not occur at all magnetic storageelements, but occurs at a non-negligible frequency in the storage devicethat integrates a large number of magnetic storage elements 10. Also,the occurrence frequency of the LPBS tends to increase under a lowtemperature environment. Thus, when the use temperature condition ismade wider, higher write voltage is necessary to achieve a sufficientwrite error rate as the storage device, resulting in increase of theelectric power consumption.

The inventors of the technology according to the present disclosure havestudied the LPBS that occurs in the magnetic storage element 10 of theSTT-MRAM, and as a result have found that the occurrence of the LPBS inthe magnetic storage element 10 changes by the external magnetic field.

Specifically, the inventors have found that, when the external magneticfield parallel to the magnetization direction to be reversed is appliedto the storage layer 18, the occurrence of the LPBS is reduced, and thedecrease of the write error rate does not become gradual. Also, theinventors have found that, when the external magnetic field antiparallelto the magnetization direction to be reversed is applied to the storagelayer 18, the influence of the LPBS increases, and the decrease of thewrite error rate becomes more gradual.

The above knowledge will be described more specifically, with referenceto FIGS. 19A to 19C. FIGS. 19A to 19C are graph diagrams that illustratea relationship between the write error rate when the write is repeatedlyperformed 10⁶ times into the magnetic storage element 10 of 1 Mbit andthe applied voltage.

Note that FIG. 19A is a result when the external magnetic field is notapplied, and FIG. 19B is a result when the external magnetic field ofapproximately 15900 A/m (200 Oe) is applied in the reversal direction ofthe magnetization of the H write, and FIG. 19C is a result when theexternal magnetic field of approximately 15900 A/m (200 Oe) is appliedin the reversal direction of the magnetization of the L write.

As illustrated in FIG. 19A, in the magnetic storage element 10, the LPBSoccurs with the increase of the applied voltage, and the decrease of thewrite error rate is gradual, in both of the H write and the L write.

However, as illustrated in FIGS. 19B and 19C, the occurrence of the LPBSis reduced, when the external magnetic field is applied to the magneticstorage element 10, and when the direction of the external magneticfield is parallel to the direction of the magnetization reversal of thestorage layer 18.

Specifically, as illustrated in FIG. 19B, the tendency of the decreaseof the write error rate does not change in the H write, when theexternal magnetic field parallel to the magnetization reversal directionof the H write is applied to the storage layer 18. Also, as illustratedin FIG. 19C, the tendency of the decrease of the write error rate doesnot change in the L write, when the external magnetic field parallel tothe magnetization reversal direction of the L write is applied to thestorage layer 18.

On the other hand, as in the L write in FIG. 19B and the H write in FIG.19C, the decrease of the write error rate becomes more gradual, when theexternal magnetic field antiparallel to the magnetization reversaldirection of the storage layer 18 is applied.

That is, according to the above knowledge, the magnetic storage element10 can reduce the occurrence of the LPBS, by applying the externalmagnetic field according to the magnetization reversal direction of thestorage layer 18 to the storage layer 18 at the time of the write to thestorage layer 18. The inventors of the technology according to thepresent disclosure have reached the accomplishment of the technologyaccording to the present disclosure, on the basis of the aboveknowledge. In the following, the technology according to the presentdisclosure that can reduce the influence on the write error rate by theLPBS in the STT-MRAM will be described in detail.

2. EMBODIMENT OF PRESENT DISCLOSURE

(2.1. Configuration of Magnetic Storage Element)

First, a configuration of a magnetic storage element according to anembodiment of the present disclosure will be described with reference toFIG. 1. FIG. 1 is an explanatory diagram that schematically illustratesa stacking structure of a magnetic storage element 1 according to thepresent embodiment.

As illustrated in FIG. 1, the magnetic storage element 1 includes afirst electrode layer 110, a magnetization assist layer 120, anon-magnetic layer 130, a magnetization fixation layer 140, amagnetization coupling layer 150, a reference layer 160, a spininjection layer 170, a storage layer 180, and a second electrode layer190. For the sake of convenience, layers 120, 140, and 160 may bereferred to as first, second, and third magnetic layers, respectively,while layers 130, 150, and 170 may be referred to as first, second andthird non-magnetic layers, respectively. However, it should beunderstood that example embodiments are not limited thereto, and thatthe terms first, second, third, and so on are interchangeable dependingupon the configuration of the magnetic storage element being described.Additional magnetic layers and non-magnetic layers (see FIG. 4) may bereferred to as fourth, fifth, and sixth magnetic/non-magnetic layers asdesired.

The magnetic storage element 1 is a STT-MRAM that stores information bythe magnetization directions of the magnetic body, as described in thebackground of the present disclosure. Also, the magnetic storage element1 is connected to the address lines that are orthogonal to each other,and is integrated to form an array, and thereby can configure a storagedevice that stores large capacity information.

The storage layer 180 is formed of ferromagnetic material in such amanner that the magnetization easy axis is directed in the perpendiculardirection to the film surface, and stores information by themagnetization directions. It is preferable that the storage layer 180 beformed of the ferromagnetic material that has the coercivity of thedegree that the magnetization direction is not reversed by disturbancefrom outside. The storage layer 180 may be formed of amorphousperpendicular magnetization material such as TbFeCo and GdFeCo, magneticmaterial that has crystal magnetic anisotropy such as CoPt and FePt, oralloy magnetic material of at least one or more selected from among Fe,Co, and Ni and at least one or more selected from among B and C, forexample.

Note that the storage layer 180 may be a single-layer film, and may be amulti-layer stack film. For example, the storage layer 180 may be astack film of a non-magnetic layer and a magnetic layer, or a stack filmof an oxide layer and a magnetic layer. The film thickness of thestorage layer 180 may be 1 nm or more and 10 nm or less, for example.

The reference layer 160 is provided at one surface side of the storagelayer 180 with the spin injection layer 170 in between. The referencelayer 160 is formed such that the magnetization direction is fixed toone direction in the ferromagnetic material, and functions as areference for the magnetization direction retained in the storage layer180. Specifically, the reference layer 160 is formed to have themagnetization fixed in the direction perpendicular to the film surfaceand toward the storage layer 180.

It is preferable that the reference layer 160 be formed of ferromagneticmaterial having a large polarizability of the magnetization and a largemagnetic resistance. The reference layer 160 may be formed of amorphousperpendicular magnetization material such as TbFeCo and GdFeCo, magneticmaterial that includes crystal magnetic anisotropy such as CoPt andFePt, or alloy magnetic material of at least one or more selected fromamong Fe, Co, and Ni and at least one or more selected from among B andC, for example. The film thickness of the reference layer 160 may be 0.5nm or more and 10 nm or less, for example.

The spin injection layer 170 is formed of non-magnetic material, and isprovided and sandwiched between the storage layer 180 and the referencelayer 160. The spin injection layer 170 reverses the magnetizationdirection of the storage layer 180, by exchanging the spin-polarizedelectron between the storage layer 180 and the reference layer 160, atthe time of write of information to the storage layer 180. Also, thespin injection layer 170 changes the electrical resistance on the basisof the magnetization direction of each of the storage layer 180 and thereference layer 160 by the magnetoresistance effect, at the time ofreadout of information from the storage layer 180. Thereby, the spininjection layer 170 can read out the change in the magnetizationdirection retained in the storage layer 180 as the change of theelectrical resistance.

The spin injection layer 170 may be formed of any of metal material andinsulator material, as long as the material is a non-magnetic body. Notethat it is preferable that the spin injection layer 170 be formed ofnon-magnetic insulator material, in order to obtain a readout signal ofa higher quality. Specifically, it is preferable that the spin injectionlayer 170 be formed of oxide material such as MgO and Al₂O₃. The filmthickness of the spin injection layer 170 may be 0.3 nm or more and 5 nmor less, for example.

When the spin injection layer 170 is formed of the non-magneticinsulator material, the storage layer 180, the spin injection layer 170,and the reference layer 160 function as what is called a ferromagnetictunnel junction (magnetic tunnel junction: MTJ) element. In this case,the magnetic resistance change rate becomes larger in the spin injectionlayer 170, and thus the change in the magnetization direction can bedetected as a larger change of the electrical resistance at the time ofthe readout of the information.

The magnetization fixation layer 140 is provided at the surface sideopposite to the surface of the reference layer 160 on which the spininjection layer 170 is provided, with the magnetization coupling layer150 in between. The magnetization fixation layer 140 is formed of themagnetic body including the ferromagnetic material having themagnetization direction antiparallel to the reference layer 160, andmagnetically couples with the reference layer 160. Thereby, themagnetization fixation layer 140 can cancel the leak magnetic field fromthe reference layer 160. Also, the magnetization fixation layer 140 canstabilize the magnetization direction of the reference layer 160 bymagnetically coupling with the reference layer 160, and improve theretention characteristics of the magnetization of the reference layer160.

It is preferable that the magnetization fixation layer 140 be formed offerromagnetic material of large coercivity. The magnetization fixationlayer 140 may be formed of amorphous perpendicular magnetizationmaterial such as TbFeCo and GdFeCo, magnetic material that has thecrystal magnetic anisotropy such as CoPt and FePt, or alloy magneticmaterial of at least one or more selected from among Fe, Co, and Ni andat least one or more selected from among B and C, for example. The filmthickness of the magnetization fixation layer 140 may be 0.5 nm or moreand 20 nm or less, for example.

The magnetization coupling layer 150 is provided and sandwiched betweenthe reference layer 160 and the magnetization fixation layer 140. Themagnetization coupling layer 150 is formed of non-magnetic material, andmagnetically couples the reference layer 160 and the magnetizationfixation layer 140. It is preferable that the magnetization couplinglayer 150 be formed of a material that makes the reference layer 160 andthe magnetization fixation layer 140 have magnetization directionsantiparallel to each other and magnetically couples the reference layer160 and the magnetization fixation layer 140 strongly. It is preferablethat the magnetization coupling layer 150 is formed of non-magneticmetal material such as Cr, Cu, Ru, Re, Rh, and Os, for example. The filmthickness of the magnetization coupling layer 150 may be 0.3 nm or moreand 2 nm or less, for example.

The magnetization assist layer 120 is provided at the surface side ofthe magnetization fixation layer 140 opposite to the surface on whichthe magnetization coupling layer 150 is provided, with the non-magneticlayer 130 in between. The magnetization assist layer 120 is formed offerromagnetic material in such a manner that the magnetization easy axisis directed in the direction perpendicular to the film surface. Also,the magnetization assist layer 120 reverses its magnetization in advanceof the storage layer 180 at the time of the write into the storage layer180, and applies the external magnetic field to the storage layer 180.Thereby, the magnetization assist layer 120 applies to the storage layer180 the external magnetic field parallel to the magnetization reversaldirection of the storage layer 180, thereby reducing the occurrence ofthe LPBS and achieving a sufficiently low write error rate withoutapplying excessively high voltage.

It is preferable that the magnetization assist layer 120 be of a smallermagnetization reversal electric current than the storage layer 180. Morespecifically, it is preferable that the magnetization assist layer 120is formed of ferromagnetic material having a smaller coercivity than thestorage layer 180. The magnetization assist layer 120 may be formed ofamorphous perpendicular magnetization material such as TbFeCo andGdFeCo, magnetic material that has crystal magnetic anisotropy such asCoPt and FePt, or alloy magnetic material of at least one or moreselected from among Fe, Co, and Ni and at least one or more selectedfrom among B and C, for example.

Note that the magnetization assist layer 120 may be a single-layer film,and may be a multi-layer stack film. For example, the magnetizationassist layer 120 may be formed of a stack film of Co and Ni, or a stackfilm of Ni and Pd. The film thickness of the magnetization assist layer120 may be 0.5 nm or more and 5 nm or less, for example.

The non-magnetic layer 130 is formed of non-magnetic material, and isprovided and sandwiched between the magnetization fixation layer 140 andthe magnetization assist layer 120. The non-magnetic layer 130 reversesthe magnetization direction of the magnetization assist layer 120, byexchanging the spin-polarized electrons between the magnetization assistlayer 120 and the magnetization fixation layer 140, at the time of writeof information into the storage layer 180.

The non-magnetic layer 130 may be formed of any of metal material andinsulator material, as long as the material is non-magnetic body. Forexample, the non-magnetic layer 130 may be formed of oxide material suchas MgO and Al₂O₃ that is the same as the spin injection layer 170, andmay be formed of non-magnetic metal material such as Cu or Au whose spinscattering length is long. Note that it is preferable that thenon-magnetic layer 130 is formed of a non-magnetic body having a smallresistance. This is to reduce the increased amount of the resistance bythe existence of the non-magnetic layer 130. The film thickness of thenon-magnetic layer 130 may be 0.3 nm or more and 5 nm or less, forexample.

Here, as illustrated in FIG. 1, when the magnetization fixation layer140 is provided on the magnetization assist layer 120, it is preferablethat the magnetization assist layer 120 and the magnetization fixationlayer 140 are formed of the material having the substantially identicaldirection of the crystal orientation and the magnetic anisotropy. Thisis because the crystalline orientation of the magnetization fixationlayer 140 is controlled to have the magnetic anisotropy in a specificdirection, by controlling the crystal orientation and the magneticanisotropy from the magnetization assist layer 120, thereby increasingthe coercivity of the magnetization fixation layer 140.

Specifically, when the magnetization fixation layer 140 is a film thathas the magnetic anisotropy in the 3-fold rotational symmetry axisdirection of a hexagonal crystal, it is preferable that themagnetization assist layer 120 is a film that has the magneticanisotropy in the 3-fold rotational symmetry axis direction of thehexagonal crystal in the same way. For example, when the magnetizationfixation layer 140 is a film made of CoPt alloy, a film made of CoNiPtalloy, or a stack film of Pt, Pd, or Ni and Co, it is preferable thatthe magnetization assist layer 120 be a film made of alloy of Pt, Cr, W,Mo, or Ni and Co, or a stack film of Pt, Pd, or Ni and Co.

Also, when the magnetization fixation layer 140 is a film that has themagnetic anisotropy in the 4-fold rotational symmetry axis direction ofa tetragonal crystal, it is preferable that the magnetization assistlayer 120 be a film that has the magnetic anisotropy in the 4-foldrotational symmetry axis direction of the tetragonal crystal in the sameway. For example, when the magnetization fixation layer 140 is a filmmade of FePt alloy, a film made of CoPt alloy, or a film made of FePdalloy, it is preferable that the magnetization assist layer 120 be afilm made of alloy of Pt, Pd, or Ni and Fe.

Note that the method for controlling the crystal orientation and themagnetic anisotropy of the magnetization fixation layer 140 is notlimited to the above. For example, the crystal orientation and themagnetic anisotropy of the magnetization fixation layer 140 may becontrolled, by using for the non-magnetic layer 130 an oxide such as MgOthat is easily oriented in the 4-fold rotational symmetry axis, and byusing the interface magnetic anisotropy generated on the interfacebetween the non-magnetic layer 130 and the magnetization fixation layer140. Thereby, the crystal orientation and the magnetic anisotropy of themagnetization fixation layer 140 can be controlled to have the magneticanisotropy in the 4-fold rotational symmetry axis direction of atetragonal crystal, without controlling the crystal orientation and themagnetic anisotropy of the magnetization assist layer 120.

The first electrode layer 110 and the second electrode layer 190 isprovided to sandwich the magnetization assist layer 120, thenon-magnetic layer 130, the magnetization fixation layer 140, themagnetization coupling layer 150, the reference layer 160, the spininjection layer 170, and the storage layer 180.

Specifically, the first electrode layer 110 is provided under themagnetization assist layer 120, and functions as a lower electrode ofthe magnetic storage element 1. The first electrode layer 110 can beformed of various types of metal materials or alloy materials. Also, thefirst electrode layer 110 may control the crystal orientation of themagnetization assist layer 120 that is stacked on the first electrodelayer 110. For example, the first electrode layer 110 may be formed ofthe metal material having the crystal structure and the magneticanisotropy substantially same as the magnetization assist layer 120. Thefilm thickness of the first electrode layer 110 may be 0.5 nm or moreand 50 nm or less, for example.

The second electrode layer 190 is provided on the storage layer 180, andfunctions as an upper electrode of the magnetic storage element 1. Also,the second electrode layer 190 may function as a protection layer of themagnetic storage element 10. The second electrode layer 190 can beformed of various types of metal materials or alloy materials. The filmthickness of the second electrode layer 190 may be 0.5 nm or more and 50nm or less, for example.

Here, the behavior at the time of write of the magnetic storage element1 according to the present embodiment will be described with referenceto FIGS. 2A and 2B. FIG. 2A is an explanatory diagram illustrating thebehavior of the magnetic storage element 1 at the time of L write inwhich the magnetization directions of the storage layer 180 and thereference layer 160 are antiparallel, and FIG. 2B is an explanatorydiagram illustrating the behavior of the magnetic storage element 1 atthe time of H write in which the magnetization directions of the storagelayer 180 and the reference layer 160 are parallel.

As illustrated in FIG. 2A, when the magnetization directions areantiparallel at the storage layer 180 and the reference layer 160, theelectric current is flowed from the second electrode layer 190 to thefirst electrode layer 110, and the electron is moved from the firstelectrode layer 110 to the second electrode layer 190, in order toreverse the magnetization direction of the storage layer 180.

In this case, the magnetization assist layer 120 receives the torquefrom the electron whose spin has become antiparallel to themagnetization direction of the magnetization fixation layer 140 by beingreflected at the magnetization fixation layer 140, and thus themagnetization of the magnetization assist layer 120 becomes antiparallelto the magnetization fixation layer 140 by the spin torque magnetizationreversal. Thereby, the magnetization assist layer 120 applies theexternal magnetic field in the direction parallel to the reference layer160 to the storage layer 180, and thereby can prompt the magnetizationreversal of the storage layer 180.

Also, as illustrated in FIG. 2B, when the magnetization directions areparallel at the storage layer 180 and the reference layer 160, theelectric current is flowed from the first electrode layer 110 to thesecond electrode layer 190, and the electron is moved from the secondelectrode layer 190 to the first electrode layer 110, in order toreverse the magnetization direction of the storage layer 180.

In this case, the magnetization assist layer 120 receives the torquefrom the electron that has the spin parallel to the magnetizationdirection of the magnetization fixation layer 140, and thus themagnetization of the magnetization assist layer 120 becomes parallel tothe magnetization fixation layer 140 by the spin torque magnetizationreversal. Thereby, the magnetization assist layer 120 applies theexternal magnetic field in the antiparallel direction to the referencelayer 160 to the storage layer 180, and thus can prompt themagnetization reversal of the storage layer 180.

Thus, even when the magnetization of the storage layer 180 is reversedin any direction, the magnetization assist layer 120 can apply theexternal magnetic field parallel to the reversal direction to thestorage layer 180. Thus, in the storage layer 180, the magnetizationreversal is prompted, and thereby the occurrence of the LPBS is reduced,and thus the magnetic storage element 1 can achieve the write error ratethat is sufficiently low even with lower applied voltage.

Note that it is preferable to make the reversal electric current of themagnetization of the magnetization assist layer 120 smaller than thestorage layer 180, to cause the magnetization assist layer 120 toreverse its magnetization in advance of the storage layer 180. That is,referring to the above equation 2, it is preferable that the index Δ ofthe thermal stability of the magnetization assist layer 120 be madesmaller than the storage layer 180. More specifically, when the volumesof the magnetization assist layer 120 and the storage layer 180 areapproximately equal, it is preferable that the coercivity of themagnetization assist layer 120 be made smaller than the storage layer180.

The magnetic storage element 1 according to the present embodimentdescribed in the above can be produced by using a publicly known method.Specifically, the magnetic storage element 1 can be produced by stackingthe layers by using various types of vacuum vapor deposition methods.For example, the magnetic storage element 1 can be produced by stackingthe layers sequentially, by using a physical vapor deposition methodsuch as a sputtering method and a molecular beam epitaxy method, and achemical vapor deposition method such as a chemical vapor deposition(CVD) method and an atomic layer deposition (ALD) method.

(2.2. Exemplary Variant)

Next, exemplary variants of the magnetic storage element 1 according tothe present embodiment will be described with reference to FIGS. 3 to 5.FIG. 3 is an explanatory diagram that schematically illustrates astacking structure of a magnetic storage element according to a firstexemplary variant, and FIG. 4 is an explanatory diagram thatschematically illustrates a stacking structure of a magnetic storageelement according to a second exemplary variant, and FIG. 5 is anexplanatory diagram that schematically illustrates a stacking structureof a magnetic storage element according to a third exemplary variant.

(First Exemplary Variant)

As illustrated in FIG. 3, in a magnetic storage element 2 according tothe first exemplary variant, the stacking order of the layers betweenthe first electrode layer 210 and the second electrode layer 290 isreversed from the magnetic storage element 1 illustrated in FIG. 1.

Specifically, in the magnetic storage element 2, a storage layer 280 isprovided on a first electrode layer 210, and a reference layer 260 isprovided on the storage layer 280 with a spin injection layer 270 inbetween, and a magnetization fixation layer 240 is provided on thereference layer 260 with a magnetization coupling layer 250 in between,and a magnetization assist layer 220 is provided on the magnetizationfixation layer 240 with a non-magnetic layer 230 in between, and asecond electrode layer 290 is provided on a magnetization assist layer220.

Note that configuration other than the stacking order of the firstelectrode layer 210, the magnetization assist layer 220, thenon-magnetic layer 230, the magnetization fixation layer 240, themagnetization coupling layer 250, the reference layer 260, the spininjection layer 270, the storage layer 280, and the second electrodelayer 290 is substantially same as the first electrode layer 110, themagnetization assist layer 120, the non-magnetic layer 130, themagnetization fixation layer 140, the magnetization coupling layer 150,the reference layer 160, the spin injection layer 170, the storage layer180, and the second electrode layer 190 of the same names that aredescribed in FIG. 1, and thus description will be omitted here.

Note that, in the magnetic storage element 2, the magnetization assistlayer 220 is provided above the magnetization fixation layer 240. Thus,the magnetization assist layer 220 can be formed without considering thecrystal orientation and the magnetic anisotropy of the magnetizationfixation layer 240.

Also, the magnetization assist layer 220 may direct the magnetizationeasy axis toward the perpendicular direction to the film surface, byusing the interface anisotropy generated at the interface with thenon-magnetic layer 230. For example, the magnetization assist layer 220can also be formed of an arbitrary ferromagnet film, by forming thenon-magnetic layer 230 out of oxide such as MgO and generating theinterface anisotropy. In this case, the magnetization assist layer 220can be formed of ferromagnet made of an alloy of at least one or moreselected from a group consisting of Fe, Co, and Ni and one or moreselected from a group consisting of B and C.

In the magnetic storage element 2 according to the first exemplaryvariant, the magnetization assist layer 220 can apply to the storagelayer 280 an external magnetic field parallel to the reversal directionof the magnetization of the storage layer 280, at the time of the writeinto the storage layer 280, thereby reducing the occurrence of the LPBSin the storage layer 280.

(Second Exemplary Variant)

As illustrated in FIG. 4, a magnetic storage element 3 according to thesecond exemplary variant is provided with reference layers (a firstreference layer 361, a second reference layer 362) and magnetizationfixation layers (a first magnetization fixation layer 341, a secondmagnetization fixation layer 342) at both sides with a storage layer 380therebetween, in addition to the magnetic storage element 1 illustratedin FIG. 1.

Specifically, in the magnetic storage element 3, the first referencelayer 361 is provided under the storage layer 380 with a first spininjection layer 371 in between, and the first magnetization fixationlayer 341 is provided under the first reference layer 361 with a firstmagnetization coupling layer 351 in between. Also, in the same way, thesecond reference layer 362 is provided on the storage layer 380 with asecond spin injection layer 372 in between, and the second magnetizationfixation layer 342 is provided on the second reference layer 362 with asecond magnetization coupling layer 352 in between.

A magnetization assist layer 320 is provided on one surface of the firstmagnetization fixation layer 341 or the second magnetization fixationlayer 342 with a non-magnetic layer 330 in between. FIG. 4 illustrates astructure in which the magnetization assist layer 320 provided at asurface side opposite to the surface of the first magnetization fixationlayer 341 on which the first magnetization coupling layer 351 isprovided, with the non-magnetic layer 330 in between. Note that it isneedless to say that the magnetization assist layer 320 may be providedat a surface side opposite to the surface of the second magnetizationfixation layer 342 on which the second magnetization coupling layer 352is provided, with the non-magnetic layer 330 in between.

Further, the first electrode layer 310 and the second electrode layer390 are provided to sandwich the above magnetization assist layer 320,the non-magnetic layer 330, the first magnetization fixation layer 341,the first magnetization coupling layer 351, the first reference layer361, the first spin injection layer 371, the storage layer 380, thesecond spin injection layer 372, the second reference layer 362, thesecond magnetization coupling layer 352, and the second magnetizationfixation layer 342.

Note that the first electrode layer 310, the magnetization assist layer320, the non-magnetic layer 330, the storage layer 380, and the secondelectrode layer 390 are substantially same (e.g., have the same materialproperties) as the first electrode layer 110, the magnetization assistlayer 120, the non-magnetic layer 130, the storage layer 180, and thesecond electrode layer 190 of the same names that are described in FIG.1, and thus description will be omitted here. Also, the firstmagnetization fixation layer 341 and the second magnetization fixationlayer 342 are substantially same as the magnetization fixation layer140, and the first magnetization coupling layer 351 and the secondmagnetization coupling layer 352 are substantially same (e.g., have thesame material properties) as the magnetization coupling layer 150, andthe first reference layer 361 and the second reference layer 362 aresubstantially same as the reference layer 160, and the first spininjection layer 371 and the second spin injection layer 372 aresubstantially same as the spin injection layer 170, and thus descriptionwill be omitted here.

In the magnetic storage element 3 according to the second exemplaryvariant, the first reference layer 361 and the second reference layer362 are provided on both surfaces of the storage layer 380 that areopposite to each other, respectively. Thereby, the magnetic storageelement 3 can impart a spin torque from each of the first referencelayer 361 and the second reference layer 362 to the storage layer 380,when writing information into the storage layer 380. Thus, the magneticstorage element 3 can reduce the reversal electric current of thestorage layer 380, and thereby information is written into the storagelayer 380 more easily.

Also, in the magnetic storage element 3 according to the secondexemplary variant as well, the magnetization assist layer 320 can applyto the storage layer 380 an external magnetic field parallel to thereversal direction of the magnetization of the storage layer 380, at thetime of write into the storage layer 380. Thus, in the magnetic storageelement 3 according to the second exemplary variant as well, themagnetization assist layer 320 can reduce the occurrence of the LPBS inthe storage layer 380.

(Third Exemplary Variant)

As illustrated in FIG. 5, in a magnetic storage element 4 according tothe third exemplary variant, reference layers (a first reference layer461, a second reference layer 462), magnetization fixation layers (afirst magnetization fixation layer 441, a second magnetization fixationlayer 442), and magnetization assist layers (a first magnetizationassist layer 421, a second magnetization assist layer 422) are providedat both sides with a storage layer 480 therebetween, in addition to themagnetic storage element 1 illustrated in FIG. 1.

Specifically, in the magnetic storage element 4, the first referencelayer 461 is provided under the storage layer 480 with a first spininjection layer 471 in between, and the first magnetization fixationlayer 441 is provided under the first reference layer 461 with a firstmagnetization coupling layer 451 in between, and the first magnetizationassist layer 421 is provided under the first magnetization fixationlayer 441 with a first non-magnetic layer 431 in between. Also, in thesame way, the second reference layer 462 is provided on the storagelayer 480 with a second spin injection layer 472 in between, and thesecond magnetization fixation layer 442 is provided on the secondreference layer 462 with a second magnetization coupling layer 452 inbetween, and the second magnetization assist layer 422 is provided onthe second magnetization fixation layer 442 with a second non-magneticlayer 432 in between.

Further, a first electrode layer 410 and a second electrode layer 490are provided to sandwich the above first magnetization assist layer 421,the first non-magnetic layer 431, the first magnetization fixation layer441, the first magnetization coupling layer 451, the first referencelayer 461, the first spin injection layer 471, the storage layer 480,the second spin injection layer 472, the second reference layer 462, thesecond magnetization coupling layer 452, the second magnetizationfixation layer 442, the second non-magnetic layer 432, and the secondmagnetization assist layer 422.

Note that the first electrode layer 410, the storage layer 480, and thesecond electrode layer 490 are substantially same as the first electrodelayer 110, the storage layer 180, and the second electrode layer 190 ofthe same names that are described in FIG. 1, and thus description willbe omitted here. Also, the first magnetization assist layer 421 and thesecond magnetization assist layer 422 are substantially same as themagnetization assist layer 120, and the first non-magnetic layer 431 andthe second non-magnetic layer 432 are substantially same as thenon-magnetic layer 130, and the first magnetization fixation layer 441and the second magnetization fixation layer 442 are substantially sameas the magnetization fixation layer 140, and the first magnetizationcoupling layer 451 and the second magnetization coupling layer 452 aresubstantially same as the magnetization coupling layer 150, and thefirst reference layer 461 and the second reference layer 462 aresubstantially same as the reference layer 160, and the first spininjection layer 471 and the second spin injection layer 472 aresubstantially same as the spin injection layer 170, and thus descriptionwill be omitted here.

In the magnetic storage element 4 according to the third exemplaryvariant, the first reference layer 461 and the second reference layer462 are provided, on both surfaces of the storage layer 480 that areopposite to each other respectively, in the same way as the magneticstorage element 3 according to the second exemplary variant. Thereby,the magnetic storage element 4 can reduce the reversal electric currentof the storage layer 480, and thereby information is written into thestorage layer 480 more easily.

Also, in the magnetic storage element 4 according to the third exemplaryvariant, the first magnetization assist layer 421 and the secondmagnetization assist layer 422 are provided at both surface sides of thestorage layer 480 that are opposite to each other, respectively.Thereby, the magnetic storage element 4 can apply an external magneticfield from each of the first magnetization assist layer 421 and thesecond magnetization assist layer 422 to the storage layer 480, whenwriting information into the storage layer 480. Thus, the magneticstorage element 4 can further reduce the occurrence of the LPBS in thestorage layer 480.

3. WORKING EXAMPLE OF PRESENT DISCLOSURE

Next, working examples and a comparative example of the magnetic storageelement according to an embodiment of the present disclosure will bedescribed with reference to FIGS. 6 to 16. Note that the workingexamples described below are just an example, and the magnetic storageelement according to the present embodiment is not limited to the belowworking examples.

Working Example 1

First, working example 1 of the magnetic storage element according tothe present embodiment will be described with reference to FIG. 6. FIG.6 is an explanatory diagram illustrating a layer structure of themagnetic storage element according to the working example 1. Themagnetic storage element according to the working example 1 correspondsto the magnetic storage element 1 illustrated in FIG. 1.

As illustrated in FIG. 6, first, the first electrode layer 110 is formedof stack films of Ta (film thickness 5 nm) and Ru (film thickness 2 nm),and the magnetization assist layer 120 is formed of CoCr (film thickness3 nm), and the non-magnetic layer 130 is formed of Cu (film thickness 1nm). Also, the magnetization fixation layer 140 is formed of CoPt (filmthickness 2 nm), and the magnetization coupling layer 150 is formed ofRu (film thickness 0.7 nm), and the reference layer 160 is formed ofFeCoB (film thickness 1 nm), and the spin injection layer 170 is formedof MgO (film thickness 0.7 nm).

Further, the storage layer 180 is formed of stack films of FeCoB (filmthickness 1.2 nm), Ta (film thickness 0.2 nm), and FeCoB (film thickness1.2 nm), and the second electrode layer 190 is formed of stack films ofMgO (film thickness 0.5 nm), Ru (film thickness 2 nm), and Ta (filmthickness 5 nm). These stack structures are formed in a cylindricalshape of diameter 50 nm, to form the magnetic storage element accordingto the working example 1.

Comparative Example

Next, the comparative example of the magnetic storage element will bedescribed with reference to FIG. 7. FIG. 7 is an explanatory diagramillustrating a layer structure of the magnetic storage element accordingto the comparative example. The comparative example corresponds to themagnetic storage element 10 illustrated in FIG. 17.

As illustrated in FIG. 7, first, the first electrode layer 11 is formedof stack films of Ta (film thickness 5 nm) and Ru (film thickness 2 nm),and the magnetization fixation layer 14 is formed of CoPt (filmthickness 2 nm), and the magnetization coupling layer 15 is formed of Ru(film thickness 0.7 nm). Also, the reference layer 16 is formed of FeCoB(film thickness 1 nm), and the spin injection layer 17 is formed of MgO(film thickness 0.7 nm).

Further, the storage layer 18 is formed of stack films of FeCoB (filmthickness 1.2 nm), Ta (film thickness 0.2 nm), and FeCoB (film thickness1.2 nm), and the second electrode layer 19 is formed of stack films ofMgO (film thickness 0.5 nm), Ru (film thickness 2 nm), and Ta (filmthickness 5 nm). These stack structures are formed in a cylindricalshape of diameter 50 nm, to form the magnetic storage element accordingto the comparative example.

(Evaluation Result)

A relationship of write error rate in relation to applied voltage isevaluated, with regard to the magnetic storage element according to theworking example 1 and the comparative example which are formed in theabove. Specifically, write is performed repeatedly 10⁶ times into 1 Mbitof the magnetic storage element according to the working example 1 andthe comparative example, and the relationship between the write errorrate in this case and the voltage between the first electrode layer andthe second electrode layer is evaluated.

The result is illustrated in FIGS. 8 and 9. FIG. 8 is a graph diagramthat illustrates the relationship between the write error rate of themagnetic storage element according to the working example 1 and theapplied voltage, and FIG. 9 is a graph diagram that illustrates therelationship between the write error rate of the magnetic storageelement according to the comparative example and the applied voltage.

Referring to FIGS. 8 and 9, in the magnetic storage element according tothe comparative example, as the applied voltage increases, the LPBS thatmakes it difficult for the write error rate to decrease occurs, ineither one of L write and H write. On the other hand, in the magneticstorage element according to the working example 1, the phenomenon thatmakes it difficult for the write error rate to decrease, which isobserved in the magnetic storage element according to the comparativeexample, is not observed in either one of L write and H write, therebyreducing the occurrence of the LPBS.

Working Examples 2 and 3

Next, working examples 2 and 3 that use FePt having the magneticanisotropy in the 4-fold rotational symmetry axis direction of thetetragonal crystal as the magnetization fixation layer 140 in theworking example 1 will be described with reference to FIGS. 10 and 11.In this case, the crystal orientation of the magnetization fixationlayer 140 can be improved, by forming the magnetization assist layer 120of a ferromagnetic material of substantially identical crystalorientation and magnetic anisotropy, or forming the non-magnetic layer130 of an oxide material that generates interface magnetic anisotropy.

FIG. 10 is an explanatory diagram illustrating a layer structure of themagnetic storage element according to the working example 2 in which themagnetization assist layer 120 is formed of a ferromagnetic materialthat has the magnetic anisotropy in the 4-fold rotational symmetry axisdirection of a tetragonal crystal.

As illustrated in FIG. 10, the first electrode layer 110 is formed ofstack films of Ta (film thickness 5 nm) and TiN (film thickness 5 nm),and the magnetization assist layer 120 is formed of a stack film ofNi/Pd (film thickness 5 nm) having the magnetic anisotropy in the 4-foldrotational symmetry axis direction of a tetragonal crystal, and thenon-magnetic layer 130 is formed of MgO (film thickness 0.5 nm), and themagnetization fixation layer 140 is formed of FePt (film thickness 2nm). The layer structure that is the same as the working example 1 canbe employed for the layer structure of and after the magnetizationcoupling layer 150, and thus description will be omitted here. Forexample, these stack structures are formed in a cylindrical shape ofdiameter 50 nm, to form the magnetic storage element according to theworking example 2.

FIG. 11 is an explanatory diagram illustrating a layer structure of themagnetic storage element according to the working example 3 in which thenon-magnetic layer 130 is formed of an oxide material that generatesinterface magnetic anisotropy.

As illustrated in FIG. 11, the first electrode layer 110 is formed of Ta(film thickness 5 nm), and the magnetization assist layer 120 is formedof FeCoB (film thickness 1 nm). Here, the non-magnetic layer 130 isformed of MgO (film thickness 0.5 nm), and the magnetization fixationlayer 140 is formed of FePt (film thickness 2 nm). Thereby, theinterface magnetic anisotropy can be generated at the interface betweenthe non-magnetic layer 130 and the magnetization fixation layer 140. Thelayer structure that is the same as the working example 1 can beemployed for the layer structure of and after the magnetization couplinglayer 150, and thus description will be omitted here. For example, thesestack structures are formed in a cylindrical shape of diameter 50 nm, toform the magnetic storage element according to the working example 3.

Working Examples 4 and 5

Next, working examples 4 and 5 of the magnetic storage element accordingto the present embodiment will be described with reference to FIGS. 12and 13. FIG. 12 is an explanatory diagram illustrating a layer structureof the magnetic storage element according to the working example 4, andFIG. 13 is an explanatory diagram illustrating a layer structure of themagnetic storage element according to the working example 5. Themagnetic storage elements according to the working examples 4 and 5correspond to the magnetic storage element 2 according to the firstexemplary variant illustrated in FIG. 3.

As illustrated in FIG. 12, the magnetic storage element according to theworking example 4 is the working example in which CoCr having themagnetic anisotropy in the 3-fold rotational symmetry axis direction ofa hexagonal crystal is used as the magnetization assist layer 220.

As illustrated in FIG. 12, first, the first electrode layer 210 isformed of stack films of Ta (film thickness 5 nm), FeCoB (film thickness0.5 nm), and MgO (film thickness 0.5 nm), and the storage layer 280 isformed of stack films of FeCoB (film thickness 1.2 nm), Ta (filmthickness 0.2 nm), and FeCoB (film thickness 1.2 nm), and the spininjection layer 270 is formed of MgO (film thickness 0.7 nm).

Also, the reference layer 260 is formed of stack films of FeCoB (filmthickness 0.5 nm) and CoCr (film thickness 2 nm), and the magnetizationcoupling layer 250 is formed of Ru (film thickness 0.7 nm), and themagnetization fixation layer 240 is formed of CoPt (film thickness 2nm). Further, the non-magnetic layer 230 is formed of Cu (film thickness1 nm), and the magnetization assist layer 220 is formed of CoCr (filmthickness 3 nm), and the second electrode layer 290 is formed of Ta(film thickness 5 nm). For example, these stack structures are formed ina cylindrical shape of diameter 50 nm, to form the magnetic storageelement according to the working example 4.

As illustrated in FIG. 13, the magnetic storage element according to theworking example 5 is the working example in which the interface magneticanisotropy is generated at the interface between the magnetizationassist layer 220 and the non-magnetic layer 230.

As illustrated in FIG. 13, first, the first electrode layer 210 isformed of stack films of Ta (film thickness 5 nm), FeCoB (film thickness0.5 nm), and MgO (film thickness 0.5 nm), and the storage layer 280 isformed of stack films of FeCoB (film thickness 1.2 nm), Ta (filmthickness 0.2 nm), and FeCoB (film thickness 1.2 nm), and the spininjection layer 270 is formed of MgO (film thickness 0.7 nm).

Also, the reference layer 260 is formed of stack films of FeCoB (filmthickness 0.5 nm) and CoCr (film thickness 2 nm), and the magnetizationcoupling layer 250 is formed of Ru (film thickness 0.7 nm), and themagnetization fixation layer 240 is formed of CoPt (film thickness 2nm). Further, the non-magnetic layer 230 is formed of MgAl₂O₄ (filmthickness 0.5 nm), and the magnetization assist layer 220 is formed ofFeCoC (film thickness 1 nm), and the second electrode layer 290 isformed of Ta (film thickness 5 nm). For example, these stack structuresare formed in a cylindrical shape of diameter 50 nm, to form themagnetic storage element according to the working example 5.

Working Examples 6 and 7

Next, working examples 6 and 7 of the magnetic storage element accordingto the present embodiment will be described with reference to FIGS. 14and 15. FIG. 14 is an explanatory diagram illustrating a layer structureof the magnetic storage element according to the working example 6, andFIG. 15 is an explanatory diagram illustrating a layer structure of themagnetic storage element according to the working example 7. Themagnetic storage elements according to the working examples 6 and 7correspond to the magnetic storage element 3 according to the secondexemplary variant illustrated in FIG. 4.

As illustrated in FIG. 14, the magnetic storage element according to theworking example 6 is the working example in which the magnetizationassist layer 320 and the non-magnetic layer 330 are provided at thefirst electrode layer 310 side with respect to the storage layer 380.

As illustrated in FIG. 14, first, the first electrode layer 310 isformed of stack films of Ta (film thickness 5 nm) and Ru (film thickness5 nm), and the magnetization assist layer 320 is formed of a stack filmof Co/Ni (film thickness 1.5 nm), and the non-magnetic layer 330 isformed of Al₂O₃ (film thickness 0.5 nm).

Also, the first magnetization fixation layer 341 is formed of CoPt (filmthickness 2 nm), and the first magnetization coupling layer 351 isformed of Ru (film thickness 0.7 nm), and the first reference layer 361is formed of FeCoB (film thickness 1 nm), and the first spin injectionlayer 371 is formed of MgO (film thickness 0.7 nm). Subsequently, thestorage layer 380 is formed of stack films of FeCoB (film thickness 1.2nm), Ta (film thickness 0.2 nm), and FeCoB (film thickness 1.2 nm).

Further, the second spin injection layer 372 is formed of MgO (filmthickness 0.5 nm), and the second reference layer 362 is formed of FePd(film thickness 2 nm), and the second magnetization coupling layer 352is formed of Rh (film thickness 0.6 nm), and the second magnetizationfixation layer 342 is formed of FePt (film thickness 2 nm), and thesecond electrode layer 390 is formed of stack films of Rh (filmthickness 1 nm) and Ta (film thickness 5 nm). For example, these stackstructures are formed in a cylindrical shape of diameter 50 nm, to formthe magnetic storage element according to the working example 6.

As illustrated in FIG. 15, the magnetic storage element according to theworking example 7 is the working example in which the magnetizationassist layer 320 and the non-magnetic layer 330 are provided at thesecond electrode layer 390 side with respect to the storage layer 380.

As illustrated in FIG. 15, first, the first electrode layer 310 isformed of stack films of Ta (film thickness 5 nm) and Pt (film thickness5 nm), and the first magnetization fixation layer 341 is formed of CoPt(film thickness 2 nm), and the first magnetization coupling layer 351 isformed of Ru (film thickness 0.7 nm), and the first reference layer 361is formed of FeCoB (film thickness 1 nm), and the first spin injectionlayer 371 is formed of MgO (film thickness 0.7 nm). Subsequently, thestorage layer 380 is formed of stack films of FeCoB (film thickness 1.2nm), Ta (film thickness 0.2 nm), and FeCoB (film thickness 1.2 nm).

Further, the second spin injection layer 372 is formed of MgO (filmthickness 0.5 nm), and the second reference layer 362 is formed of FeCoB(film thickness 1 nm), and the second magnetization coupling layer 352is formed of Re (film thickness 0.5 nm), and the second magnetizationfixation layer 342 is formed of a stack film of Co/Pd (film thickness 3nm). Subsequently, the non-magnetic layer 330 is formed of Au (filmthickness 1 nm), and the magnetization assist layer 320 is formed of astack film of Co/Pd (film thickness 1.5 nm), and the second electrodelayer 390 is formed of stack films of Au (film thickness 1 nm) and Ta(film thickness 5 nm). For example, these stack structures are formed ina cylindrical shape of diameter 50 nm, to form the magnetic storageelement according to the working example 7.

Working Example 8

Next, working example 8 of the magnetic storage element according to thepresent embodiment will be described with reference to FIG. 16. FIG. 16is an explanatory diagram illustrating a layer structure of the magneticstorage element according to the working example 8. The magnetic storageelement according to the working example 8 corresponds to the magneticstorage element 4 according to the third exemplary variant illustratedin FIG. 5.

As illustrated in FIG. 16, first, the first electrode layer 410 isformed of Ta (film thickness 5 nm), and the first magnetization assistlayer 421 is formed of FeCoB (film thickness 1 nm), and the firstnon-magnetic layer 431 is formed of MgO (film thickness 0.5 nm).Subsequently, the first magnetization fixation layer 441 is formed ofFePt (film thickness 1 nm), and the first magnetization coupling layer451 is formed of Ru (film thickness 0.7 nm), and the first referencelayer 461 is formed of FePt (film thickness 1.2 nm), and the first spininjection layer 471 is formed of MgO (film thickness 0.7 nm).Subsequently, the storage layer 480 is formed of FePd (film thickness 2nm).

Further, the second spin injection layer 472 is formed of MgO (filmthickness 0.5 nm), and the second reference layer 462 is formed of FePt(film thickness 1 nm), and the second magnetization coupling layer 452is formed of Ru (film thickness 0.7 nm), and the second magnetizationfixation layer 442 is formed of FePt (film thickness 1.2 nm).Subsequently, the second non-magnetic layer 432 is formed of MgO (filmthickness 0.5 nm), and the second magnetization assist layer 422 isformed of FeCoB (film thickness 1 nm), and the second electrode layer490 is formed of Ta (film thickness 5 nm). For example, these stackstructures are formed in a cylindrical shape of diameter 50 nm, to formthe magnetic storage element according to the working example 8.

The relationship of the write error rate in relation to the appliedvoltage is evaluated for the magnetic storage elements according to theworking examples 2 to 8 described above in the same way as the workingexample 1, and as a result it is found that the occurrence of the LPBSis reduced in both of the L write and the H write.

4. CONCLUSION

As described above, in the magnetic storage element according to anembodiment of the present disclosure, when information is written, anexternal magnetic field parallel to the magnetization reversal directionof the storage layer is applied to the storage layer by themagnetization assist layer, thereby reducing the occurrence of the LPBSthat makes it difficult to decrease the write error rate. Thus, themagnetic storage element according to the present embodiment decreasesthe write error rate sufficiently, without increasing the appliedvoltage at the time of write excessively, thereby reducing the electricpower consumption.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

Further, the effects described in this specification are merelyillustrative or exemplified effects, and are not limitative. That is,with or in the place of the above effects, the technology according tothe present disclosure may achieve other effects that are clear to thoseskilled in the art based on the description of this specification.

Additionally, the present technology may also be configured as below.

(1)

A magnetic storage element including:

a storage layer that has a magnetization easy axis in a perpendiculardirection to a film surface, a magnetization direction of the storagelayer being variable;

a reference layer provided at least one surface side of the storagelayer with a non-magnetic layer in between, and having magnetizationwhose direction is fixed in one direction perpendicular to a filmsurface;

a magnetization fixation layer provided at a surface side opposite to asurface of the reference layer at which the storage layer is provided,with a non-magnetic layer in between, and having magnetization whosedirection is fixed in an antiparallel direction to a magnetizationdirection of the reference layer; and

a magnetization assist layer provided at a surface side opposite to asurface of the magnetization fixation layer at which the reference layeris provided, with a non-magnetic layer in between, and having amagnetization easy axis in a perpendicular direction to a film surface,wherein change in a magnetization direction is easier than in thestorage layer.

(2)

The magnetic storage element according to (1), wherein

an electric current amount that reverses magnetization of themagnetization assist layer is smaller than an electric current amountthat reverses magnetization of the storage layer.

(3)

The magnetic storage element according to (1) or (2), wherein

the magnetization assist layer is provided under the magnetizationfixation layer with a non-magnetic layer in between, and

the magnetization fixation layer and the magnetization assist layer havesubstantially identical directions of crystal orientation and magneticanisotropy.

(4)

The magnetic storage element according to (3), wherein

the magnetization fixation layer is a film made of a CoPt alloy, a filmmade of a CoNiPt alloy, or stack films of Pt, Pd, or Ni and Co, and

the magnetization assist layer is a film made of an alloy of Cr, W, Mo,or Ni and Co, or stack films of Pt, Pd, or Ni and Co.

(5)

The magnetic storage element according to (3), wherein

the magnetization fixation layer is a film made of an FePt alloy, a filmmade of a CoPt alloy, or a film made of an FePd alloy, and

the magnetization assist layer is a film made of an alloy of Pt, Pd, orNi and Fe.

(6)

The magnetic storage element according to (1) or (2), wherein

the magnetization assist layer is provided under the magnetizationfixation layer with a non-magnetic layer in between,

the magnetization fixation layer is a film made of an FePt alloy, a filmmade of a CoPt alloy, or a film made of an FePd alloy, and

the non-magnetic layer between the magnetization fixation layer and themagnetization assist layer is a film made of an oxide material.

(7)

The magnetic storage element according to (1) or (2), wherein

the magnetization assist layer is provided on the magnetization fixationlayer with a non-magnetic layer in between,

the non-magnetic layer between the magnetization fixation layer and themagnetization assist layer is a film made of an oxide material, and

the magnetization assist layer is a film made of an alloy of at leastone or more selected from a group consisting of Fe, Co, and Ni and atleast one or more selected from a group consisting of B and C.

(8)

The magnetic storage element according to any one of (1) to (7), wherein

the reference layer and the magnetization fixation layer are provided ateach of both surface sides of the storage layer that are opposite toeach other.

(9)

The magnetic storage element according to (8), wherein

the magnetization assist layer is provided at each of both surface sidesof the storage layer that are opposite to each other, with the referencelayer and the magnetization fixation layer in between.

(10)

The magnetic storage element according to any one of (1) to (9), wherein

the non-magnetic layer between the storage layer and the reference layerincludes an oxide material having an insulation property.

(11)

The magnetic storage element according to any one of (1) to (10),wherein

the non-magnetic layer between the reference layer and the magnetizationfixation layer includes a non-magnetic metal material.

(12)

A magnetic storage element including:

a storage layer that stores information by a magnetization direction;

a reference layer whose magnetization direction is fixed, the referencelayer serving as a reference for the magnetization direction of thestorage layer;

a magnetization fixation layer that magnetically couples with thereference layer; and a magnetization assist layer in which change in amagnetization direction is easier than in the storage layer,

wherein when information is written into the storage layer by a spintorque generated by an electric current that flows through the storagelayer, the reference layer, the magnetization fixation layer, and themagnetization assist layer, the magnetization assist layer reversesmagnetization in a parallel direction to the magnetization directionwritten into the storage layer, and applies an external magnetic fieldto the storage layer.(13)The magnetic storage element according to (12), wherein themagnetization assist layer is provided under the magnetization fixationlayer with a non-magnetic layer in between, andthe magnetization fixation layer and the magnetization assist layer havesubstantially identical directions of crystal orientation and magneticanisotropy.(14)The magnetic storage element according to (13), whereinthe magnetization fixation layer is a film made of a CoPt alloy, a filmmade of a CoNiPt alloy, or stack films of Pt, Pd, or Ni and Co, andthe magnetization assist layer is a film made of an alloy of Cr, W, Mo,or Ni and Co, or stack films of Pt, Pd, or Ni and Co.(15)The magnetic storage element according to (13), whereinthe magnetization fixation layer is a film made of an FePt alloy, a filmmade of a CoPt alloy, or a film made of an FePd alloy, andthe magnetization assist layer is a film made of an alloy of Pt, Pd, orNi and Fe.(16)The magnetic storage element according to (12), whereinthe magnetization assist layer is provided under the magnetizationfixation layer with a non-magnetic layer in between,the magnetization fixation layer is a film made of an FePt alloy, a filmmade of a CoPt alloy, or a film made of an FePd alloy, andthe non-magnetic layer between the magnetization fixation layer and themagnetization assist layer is a film made of an oxide material.(17)The magnetic storage element according to (12), whereinthe magnetization assist layer is provided on the magnetization fixationlayer with a non-magnetic layer in between,the non-magnetic layer between the magnetization fixation layer and themagnetization assist layer is a film made of an oxide material, andthe magnetization assist layer is a film made of an alloy of at leastone or more selected from a group consisting of Fe, Co, and Ni and atleast one or more selected from a group consisting of B and C.Additionally, the present technology may also be configured as below.(1)A magnetic storage element, comprising:a first magnetic layer having a magnetization easy axis in a directionperpendicular to a surface of the first magnetic layer;a first non-magnetic layer on the first magnetic layer;a second magnetic layer on the first non-magnetic layer and having afixed magnetization direction;a second non-magnetic layer on the second magnetic layer;a third magnetic layer on the second non-magnetic layer and having afixed magnetization direction perpendicular to a surface of the thirdmagnetic layer; anda third non-magnetic layer on the third magnetic layer;a storage layer on the third non-magnetic layer and having a variablemagnetization direction with a magnetization easy axis in a directionperpendicular to a surface of the storage layer,wherein the fixed magnetization direction of the second magnetic layeris in an antiparallel direction to the fixed magnetization direction ofthe third magnetic layer, and wherein change in a magnetizationdirection of the first magnetic layer is easier than in the storagelayer.(2)The magnetic storage element according to (1), whereinan electric current amount that reverses magnetization of the firstmagnetic layer is smaller than an electric current amount that reversesmagnetization of the storage layer.(3)The magnetic storage element according to (1), whereinthe second magnetic layer and the first magnetic layer havesubstantially identical directions of crystal orientation and magneticanisotropy.(4)The magnetic storage element according to (3), whereinthe second magnetic layer is a film made of a CoPt alloy, a film made ofa CoNiPt alloy, or stacked films of Pt, Pd, or Ni and Co, andthe first magnetic layer is a film made of an alloy of Cr, W, Mo, or Niand Co, or stacked films of Pt, Pd, or Ni and Co.(5)The magnetic storage element according to (3), whereinthe second magnetic layer is a film made of an FePt alloy, a film madeof a CoPt alloy, or a film made of an FePd alloy, andthe first magnetic layer is a film made of an alloy of Pt, Pd, or Ni andFe.(6)The magnetic storage element according to (1), whereinthe second magnetic layer is a film made of an FePt alloy, a film madeof a CoPt alloy, or a film made of an FePd alloy, andthe first non-magnetic layer is a film made of an oxide material.(7)The magnetic storage element according to (1), whereinthe first non-magnetic layer is a film made of an oxide material, andthe first magnetic layer is a film made of an alloy of at least one ormore of Fe, Co, and Ni and at least one or more of B and C.(8)The magnetic storage element according to (1), further comprising:a fourth magnetic layer on the storage layer; anda fifth magnetic layer on the fourth magnetic layer, wherein the fourthmagnetic layer has the same material properties as the third magneticlayer, and wherein the fifth magnetic layer has the same properties asthe second magnetic layer.(9)The magnetic storage element according to (8), further comprising:a sixth magnetic layer on the fifth magnetic layer, wherein the sixthmagnetic layer has the same material properties as the first magneticlayer.(10)The magnetic storage element according to (1), whereinthe third non-magnetic layer includes an oxide material having aninsulation property.(11)The magnetic storage element according to (1), whereinthe second non-magnetic layer includes a non-magnetic metal material.(12)A magnetic storage element, comprising:a storage layer that stores information based on a magnetizationdirection of the storage layer;a reference layer whose magnetization direction is fixed, the referencelayer serving asa reference for the magnetization direction of the storage layer;a magnetization fixation layer that magnetically couples with thereference layer; anda magnetization assist layer in which change in a magnetizationdirection is easier than in the storage layer,wherein when the information is written into the storage layer by a spintorque generated by an electric current that flows through the storagelayer, the reference layer, the magnetization fixation layer, and themagnetization assist layer, the magnetization assist layer reversesmagnetization in a direction parallel to the magnetization directionwritten to the storage layer, and applies an external magnetic field tothe storage layer.(13)The magnetic storage element according to (12), further comprising:a non-magnetic layer between the magnetization assist layer and themagnetization fixation layer, wherein the magnetization fixation layerand the magnetization assist layer have substantially identicaldirections of crystal orientation and magnetic anisotropy.(14)The magnetic storage element according to (13), whereinthe magnetization fixation layer is a film made of a CoPt alloy, a filmmade of a CoNiPt alloy, or stacked films of Pt, Pd, or Ni and Co, andthe magnetization assist layer is a film made of an alloy of Cr, W, Mo,or Ni and Co, or stacked films of Pt, Pd, or Ni and Co.(15)The magnetic storage element according to claim 13), whereinthe magnetization fixation layer is a film made of an FePt alloy, a filmmade of a CoPt alloy, or a film made of an FePd alloy, andthe magnetization assist layer is a film made of an alloy of Pt, Pd, orNi and Fe.(16)The magnetic storage element according to (12), further comprising:a non-magnetic layer between the magnetization assist layer and themagnetization fixation layer, whereinthe magnetization fixation layer is a film made of an FePt alloy, a filmmade of a CoPt alloy, or a film made of an FePd alloy, andthe non-magnetic layer is a film made of an oxide material.(17)The magnetic storage element according to (12), further comprising:a non-magnetic layer between the magnetization assist layer and themagnetization fixation layer, whereinthe non-magnetic layer is a film made of an oxide material, andthe magnetization assist layer is a film made of an alloy of at leastone or more of Fe, Co, and Ni and at least one or more of B and C.(18)A magnetic storage element comprising:a storage layer that stores information based on a magnetizationdirection of the storage layer;a first magnetic layer whose magnetization direction is fixed, the firstmagnetic layer serving as a reference for the magnetization direction ofthe storage layer;a second magnetic layer that magnetically couples with the firstmagnetic layer; anda third magnetic layer in which change in a magnetization direction iseasier than in the storage layer,wherein when the information is written to the storage layer by a spintorque generated by an electric current that flows through the storagelayer, the first magnetic layer, the second magnetic layer, and thethird magnetic layer, the third magnetic layer reverses magnetization ina direction parallel to the magnetization direction written to thestorage layer, and applies an external magnetic field to the storagelayer.(19)The magnetic storage element according to (18), further comprising:a non-magnetic layer between the third magnetic layer and the secondmagnetic layer, wherein the second magnetic layer and the third magneticlayer have substantially identical directions of crystal orientation andmagnetic anisotropy.(20)The magnetic storage element according to (19), whereinthe second magnetic layer is a film made of a CoPt alloy, a film made ofa CoNiPt alloy, or stacked films of Pt, Pd, or Ni and Co, andthe third magnetic layer is a film made of an alloy of Cr, W, Mo, or Niand Co, or stacked films of Pt, Pd, or Ni and Co.

REFERENCE SIGNS LIST

-   -   1 magnetic storage element    -   110 first electrode layer    -   120 magnetization assist layer    -   130 non-magnetic layer    -   140 magnetization fixation layer    -   150 magnetization coupling layer    -   160 reference layer    -   170 spin injection layer    -   180 storage layer    -   190 second electrode layer

What is claimed is:
 1. A magnetic storage element, comprising: a firstmagnetic layer having a magnetization easy axis in a directionperpendicular to a surface of the first magnetic layer; a firstnon-magnetic layer on the first magnetic layer; a second magnetic layeron the first non-magnetic layer and having a fixed magnetizationdirection; a second non-magnetic layer on the second magnetic layer; athird magnetic layer on the second non-magnetic layer and having a fixedmagnetization direction perpendicular to a surface of the third magneticlayer; and a third non-magnetic layer on the third magnetic layer; astorage layer on the third non-magnetic layer and having a variablemagnetization direction with a magnetization easy axis in a directionperpendicular to a surface of the storage layer, wherein the fixedmagnetization direction of the second magnetic layer is in anantiparallel direction to the fixed magnetization direction of the thirdmagnetic layer, wherein the fixed magnetization direction of the thirdmagnetic layer is toward the storage layer, wherein change in amagnetization direction of the first magnetic layer is easier than inthe storage layer, and wherein the first magnetic layer includes atleast one of TbFeCo and GdFeCo.
 2. The magnetic storage elementaccording to claim 1, wherein an electric current amount that reversesmagnetization of the first magnetic layer is smaller than an electriccurrent amount that reverses magnetization of the storage layer.
 3. Themagnetic storage element according to claim 1, wherein the secondmagnetic layer and the first magnetic layer have substantially identicaldirections of crystal orientation and magnetic anisotropy.
 4. Themagnetic storage element according to claim 3, wherein the secondmagnetic layer is a film made of a CoPt alloy, a film made of a CoNiPtalloy, or stacked films of Pt, Pd, or Ni and Co.
 5. The magnetic storageelement according to claim 3, wherein the second magnetic layer is afilm made of an FePt alloy, a film made of a CoPt alloy, or a film madeof an FePd alloy.
 6. The magnetic storage element according to claim 1,wherein the second magnetic layer is a film made of an FePt alloy, afilm made of a CoPt alloy, or a film made of an FePd alloy, and thefirst non-magnetic layer is a film made of an oxide material.
 7. Themagnetic storage element according to claim 1, wherein the firstnon-magnetic layer is a film made of an oxide material.
 8. The magneticstorage element according to claim 1, further comprising: a fourthmagnetic layer on the storage layer; and a fifth magnetic layer on thefourth magnetic layer, wherein the fourth magnetic layer has the samematerial properties as the third magnetic layer, and wherein the fifthmagnetic layer has the same properties as the second magnetic layer. 9.The magnetic storage element according to claim 8, further comprising: asixth magnetic layer on the fifth magnetic layer, wherein the sixthmagnetic layer has the same material properties as the first magneticlayer.
 10. The magnetic storage element according to claim 1, whereinthe third non-magnetic layer includes an oxide material having aninsulation property.
 11. The magnetic storage element according to claim1, wherein the second non-magnetic layer includes a non-magnetic metalmaterial.
 12. A magnetic storage element, comprising: a storage layerthat stores information based on a magnetization direction of thestorage layer, wherein the storage layer has a magnetization easy axisin a direction perpendicular to a surface of the storage layer; areference layer whose magnetization direction is fixed in a directiontoward the storage layer and perpendicular to a surface of the referencelayer, the reference layer serving as a reference for the magnetizationdirection of the storage layer; a magnetization fixation layer thatmagnetically couples with the reference layer and having a fixedmagnetization direction that is antiparallel to the fixed magnetizationdirection of the reference layer; and a magnetization assist layer inwhich change in a magnetization direction is easier than in the storagelayer, wherein the magnetization assist layer includes at least one ofTbFeCo and GdFeCo, and wherein the magnetization assist layer has amagnetization easy axis in a direction perpendicular to a surface of themagnetization assist layer, wherein when the information is written intothe storage layer by a spin torque generated by an electric current thatflows through the storage layer, the reference layer, the magnetizationfixation layer, and the magnetization assist layer, the magnetizationassist layer reverses magnetization in a direction parallel to themagnetization direction written to the storage layer, and applies anexternal magnetic field to the storage layer.
 13. The magnetic storageelement according to claim 12, further comprising: a non-magnetic layerbetween the magnetization assist layer and the magnetization fixationlayer, wherein the magnetization fixation layer and the magnetizationassist layer have substantially identical directions of crystalorientation and magnetic anisotropy.
 14. The magnetic storage elementaccording to claim 13, wherein the magnetization fixation layer is afilm made of a CoPt alloy, a film made of a CoNiPt alloy, or stackedfilms of Pt, Pd, or Ni and Co.
 15. The magnetic storage elementaccording to claim 13, wherein the magnetization fixation layer is afilm made of an FePt alloy, a film made of a CoPt alloy, or a film madeof an FePd alloy.
 16. The magnetic storage element according to claim12, further comprising: a non-magnetic layer between the magnetizationassist layer and the magnetization fixation layer, wherein themagnetization fixation layer is a film made of an FePt alloy, a filmmade of a CoPt alloy, or a film made of an FePd alloy, and thenon-magnetic layer is a film made of an oxide material.
 17. The magneticstorage element according to claim 12, further comprising: anon-magnetic layer between the magnetization assist layer and themagnetization fixation layer, wherein the non-magnetic layer is a filmmade of an oxide material.
 18. A magnetic storage element comprising: astorage layer that stores information based on a magnetization directionof the storage layer, wherein the storage layer has a magnetization easyaxis in a direction perpendicular to a surface of the storage layer; afirst magnetic layer whose magnetization direction is fixed in adirection toward the storage layer and perpendicular to a surface of thefirst magnetic layer, the first magnetic layer serving as a referencefor the magnetization direction of the storage layer; a second magneticlayer that magnetically couples with the first magnetic layer and thathas a fixed magnetization direction that is antiparallel to the fixedmagnetization direction of the first magnetic layer; and a thirdmagnetic layer having a magnetization easy axis in a directionperpendicular to a surface of the third magnetic layer and in whichchange in a magnetization direction is easier than in the storage layer,wherein the third magnetic layer includes at least one of TbFeCo andGdFeCo, wherein when the information is written to the storage layer bya spin torque generated by an electric current that flows through thestorage layer, the first magnetic layer, the second magnetic layer, andthe third magnetic layer, the third magnetic layer reversesmagnetization in a direction parallel to the magnetization directionwritten to the storage layer, and applies an external magnetic field tothe storage layer.
 19. The magnetic storage element according to claim18, further comprising: a non-magnetic layer between the third magneticlayer and the second magnetic layer, wherein the second magnetic layerand the third magnetic layer have substantially identical directions ofcrystal orientation and magnetic anisotropy.
 20. The magnetic storageelement according to claim 19, wherein the second magnetic layer is afilm made of a CoPt alloy, a film made of a CoNiPt alloy, or stackedfilms of Pt, Pd, or Ni and Co.